You will find The Threader won't score the Ceramic it might discolour it in fact ceramic is a Very Hard Wear Resistant Material which can Withstand Enormous Heat however the opposite will occur The Threader over time will wear depending on how much use it's given.
There is one disadvantage Ceramic is Very Hard & if The Bobbin Holder is Dropped it can be Damaged or Broken so I'd suggest don't use it on any Hard Floors.
Brian.